Cold then warm is either low gas or the compressor clutch cutting out on pressure. Warm from the moment you start is usually gas that has already gone, and gas does not get used up: if it is low, it leaked.
We put gauges on both sides, read the pressures, then vacuum the system and watch whether it holds. Dye goes in with the charge so that when you come back we can find the leak with a lamp instead of guessing.
How we tell: A rattle or a click from the front of the engine when the AC cuts in.
In this order
The same three steps as every car that comes through the door: the check, then the quote, then your old parts.
JMD 3,500comes off the bill
Pressure test on the cooling system, gauges on the AC, dye if it is losing gas.
0JMD 60,000120,000
Whatever comes off your car is bagged with your registration on it and handed to you when you collect. It is the simplest proof that the part we charged you for was the part we changed.